The present invention relates to a method and an apparatus for an internal combustion engine.
Turbochargers are well known and widely used with combustion engines for purpose of increasing power output, decreasing fuel consumption and emissions, and compensating for air density loss at high altitudes. Generally, turbochargers supply an increased charge air supply for the combustion process than can otherwise be induced through natural aspiration by utilizing exhaust gas energy to drive an air compressor. This increased air supply allows more fuel to be burned, thereby increasing power and output not otherwise obtainable from an engine having a given cylinder displacement under natural aspiration conditions. Variable geometry turbochargers (VGTs) allow the intake airflow to be optimized over a range of engine speeds. This may be accomplished by changing the angle of the inlet guide vanes on the turbine stator. An optimal position for the inlet guide vanes is determined from a combination of desired torque response, fuel economy, and emission requirement.
EGR systems are used to reduce NOx emissions by—increasing the dilution fraction in the intake manifold. EGR is typically accomplished with an EGR valve that connects the intake manifold with the exhaust manifold.
In the cylinders, the recirculated exhaust gas acts as an inert gas, thus lowering the flame and in-cylinder gas temperature and, hence, decreasing the formation of NOx. On the other hand, the recirculated exhaust gas displaces fresh air and reduces the air-to-fuel ratio of the in-cylinder mixture.
At medium to high engine speeds, there is an abundance of energy in the engine exhaust gas stream and, over this operating speed range, the turbocharger is capable of supplying the engine cylinders with all the air needed for efficient combustion and maximum power and torque output for a given engine construction. In certain applications, however, an exhaust stream waste gate, i.e., vent, is needed to bleed off excess energy in the engine exhaust stream before it enters the turbocharger turbine to prevent the engine from being overcharged. Typically, the waste gate is set to open at a pressure below which undesirable predetonation or an unacceptable high internal engine cylinder pressure is generated.
A particular problem with turbocharged diesel engines is poor acceleration, particularly from idle or low engine speeds. This “turbo-lag” is due to the time delay associated with filling the intake manifold with enough fresh air to support the amount of fuel required to satisfy the operator's torque demand. To meet this requirement, however, the delivered fuel often must be limited as a function of the available air in order to maintain the air-to fuel ratio above the threshold at which visible smoke occurs. The rate at which the air supply can be increased is limited by the dynamics of the turbocharger and the transport delay between the turbocharger compressor and the intake manifold of the engine.
To improve acceleration, some engine control systems use a transient detection feature to turn off the feedback control to the EGR and close the EGR valve when fuel limiting is active. This is done to provide as much fresh air as possible to the intake manifold so that the maximum amount of fuel can be injected without violating the air/fuel threshold at which visible smoke occurs.
There is still a need for an improved internal combustion engine system which improves engine performance, low-speed engine response and reduced emission characteristics of a conventional internal combustion engine and an improved turbo charging system for controlling and optimizing turbocharged engine performance.
It is desirable to overcome the problems of prior systems and to provide an improved internal combustion engine and turbo charging system for improved engine performance at least at transient conditions.
According to a first aspect of the invention it is provided a method for reducing turbolag in a turbocharged internal combustion engine comprising an inlet manifold, an exhaust manifold, an exhaust gas recirculation (EGR) valve and a Variable Geometry Turbine (VGT) turbo unit.
Said method comprising the steps of demanding torque for shifting the internal combustion engine from a stationary engine mode to a transient engine mode; closing the EGR valve at a positive pressure difference during said transient engine mode; repositioning guide vanes of the VGT turbo unit from a first position when in said stationary engine mode to a second position at said positive pressure difference during said transient engine mode; increasing a duration of overlapping of at least one inlet valve and at least one outlet valve provided in a cylinder head of said internal combustion engine from a first duration when in said stationary engine mode to a second duration at said positive pressure difference during said transient engine mode for increasing the amount of air flowing from the inlet manifold to the exhaust manifold and thereby increasing acceleration of a turbine of said VGT turbo unit.
An advantage of this embodiment of the present invention is a better response, particularly for a diesel engine with VGT turbo used in a wheel loader.
In another example embodiment of the present invention said increasing of duration of at least one inlet valve and at least one outlet valve comprising the steps of providing a first cam lobe on a rotatable camshaft for interacting with a main rocker arm serving to transmit the movement of said first cam lobe to a first inlet valve; providing at least one second cam lobe spaced apart from said first cam lobe, where said second cam lobe is actable on a secondary rocker arm servable to transmit the movement of said second cam lobe to said first inlet valve during each revolution of the camshaft; switching said secondary rocker arm between at least two different working positions.
An advantage of this embodiment of the present invention is that it is a compact and requires very little space.
Another advantage of this embodiment is that said switching may be performed dynamically during the use of the internal combustion engine, which means that the overlap of the inlet and outlet valves may be varied at any time on demand.
In another example embodiment of the present invention said at least second cam lobe is provided laterally spaced apart from said first cam lobe on said rotatable camshaft.
An advantage of this embodiment is that a single camshaft may be used with no or very little design changes compared to a standard camshaft for the same engine.
In another example embodiment of the present invention said second cam lobe is provided on a second camshaft and said first cam lobe is provided on a first camshaft.
An advantage of this embodiment is that it may give a greater freedom of design alternatives than using a single camshaft regarding the design of the cam lobes, positioning of the cam lobes and the design of the valve train.
In another example embodiment of the present invention said second cam lobe is asymmetrical.
In still another example embodiment of the present invention said method further comprising the step of: switching said secondary rocker arm between at least two different positions with a hydraulic circuit comprising a fluid source, a hydraulic piston, which is displaceable in a hydraulic cylinder.
An advantage of this embodiment of the present invention is that an available hydraulic pressure may be used for said switching of said secondary rocker arm between said at least two different positions.
In still another example embodiment of the present invention said method further comprising the step of: switching said secondary rocker arm between at least two different positions with an electromagnetic circuit comprising an electromagnetic source and a piston displaceable in a cylinder, where said piston is movable by means of applying an electromagnetic field.
An advantage of this embodiment of the present invention is that the switching may be very quick and that the electromagnetic circuit may require very little space.
In still another example embodiment of the present invention said method further comprising the step of: switching said secondary rocker arm between at least two different positions with an air pressure circuit comprising an air pressure source and a piston displaceable in a cylinder, where said piston is movable by means of applying an air pressure.
An advantage of this embodiment of the present invention is that an available air pressure may be used for said switching of said secondary rocker arm between said at least two different positions.
According to another aspect of the present invention it is provided a computer readable memory comprising a program code for performing the method for reducing turbolag in a turbocharged internal combustion engine.
According to still another aspect of the present invention it is provided a vehicle comprising the computer readable memory comprising a program code for performing the method for reducing turbolag in a turbocharged internal combustion engine.
According to yet another aspect of the present invention it is provided an apparatus for reducing turbolag in a turbocharged internal combustion engine comprising an inlet manifold, an exhaust manifold, an exhaust gas recirculation (EGR) valve and a Variable Geometry Turbine (VGT) turbo unit. Said apparatus comprising: means for demanding torque for shifting the internal combustion engine from a stationary engine mode to a transient engine mode; means for closing the EGR valve at a positive pressure difference during said transient engine mode; means for repositioning guide vanes of the VGT turbo unit from a first position when in said stationary engine mode to a second position at said positive pressure difference during said transient engine mode; means for increasing a duration of overlapping of at least one inlet valve and at least one outlet valve provided in a cylinder head of said internal combustion engine from a first duration when in said stationary engine mode to a second duration at said positive pressure difference during said transient engine mode for increasing the amount of air flowing from the inlet manifold to the exhaust manifold and thereby increasing acceleration of a turbine of said VGT turbo unit.